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DR. LUMA NASSRAT
ASSISSTANT LECTURER, DEPARTMENT OF
PROSTHODONTICS
COLLEGE OF DENTISTRY
TIKRIT UNIVERSITY
Surveying Tools:
ANALYSING ROD:
▪ Used for preliminary survey of the cast.
▪ Assessment of degree of undercuts on hard & soft
tissues.
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RPD LEC.5 | PROSTHODONTICS | 12-11-2018
Surveying Part 23RD GRADE
LEC. 5
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▪ Assessment of angulation of teeth.
▪ In distal extension cases, allows judgement of whether the
distal abutment undercuts are sufficient to indicate that a
tilt
may be beneficial.
CARBON MARKER:
▪ Basically, allows visualization of the analyzing rod’s
work.
▪ Used for drawing survey lines around all teeth involved in
clasp design or that have proximal undercuts to be
eliminated.
▪ To mark the extent of bony/soft tissue undercuts for
prosthetic
mouth preparation if required.
▪ Light pressure without erosion.
UNDERCUT GAUGES:
▪ Used to measure the location and horizontal depth of
undercuts on the analyzed and marked teeth in three
dimensions.
Stewert – o.o1”,0.015”,0.02”
McCracken-0.01”,0.02”,0.03”
▪ Same shank, only the size of the tip/bead varies.
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WAX TRIMMERS:
▪ Used to trim off excessive wax while surveying the wax
patterns.
▪ To prevent overcontoured blockout of unfavorable
undercuts.
▪ To demarcate the exact planned clasp arm location to be
duplicated.
Survey Process:
The surveying process is composed of several phases. Each
phase is important in successful removable partial denture
therapy.
The phases are:
Identifying the most favorable tilt
• The cast is affixed to the surveying table. The ball and-
socket
design of the table permits the practitioner to change the tilt
of
the cast to the favorable tilt. (The tilt of the cast is
described
from the viewpoint of a person looking at its posterior
surface).
• If the anterior of the cast is lowered anterior tilt.
• If the posterior is lowered posterior tilt.
• If the right side is lowered right tilt.
• And if the left side is lowered left tilt
• Extreme tilts should be avoided.
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There are four critical factors that must be considered when
determining the most favorable tilt of a dental cast. These
factors are
in order of importance:
(1) the presence of suitable undercuts.
(2) the elimination of hard and soft tissue interferences
(3) the creation of desirable esthetics.
(4) the establishment of appropriate guiding planes.
Retentive Undercuts:• The retentive undercuts must be present on
the abutment teeth
when the cast displays a horizontal tilt. This is essential
because
dislodging forces are always directed perpendicular to the
occlusal plane.
!• Each abutment is examined for retentive undercuts using
analyzing rod.
• If retentive undercuts are not present, they must be created
in
the mouth. Either by recontouring enamel surfaces, or by
placing fixed restorations in extensive cases. These
restorations
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must be carefully planned and completed prior to RPD
fabrication.
• Ideally, undercuts may be at the mesiobuccal line angle,
the
distobuccal line angle, or the midfacial surface.
• In all cases, the undercut should be in the apical third of
the
clinical crown.
• When the existence of retentive undercuts has been verified,
the
tilt may be changed to optimize the undercut on any tooth.
• Changing the tilt to alter the position of the undercut on
one
tooth will affect the positions of the undercuts on the
remaining
teeth. The tilt is normally changed so that a retentive clasp
will
be positioned no farther occlusally or incisally than the
junction
of the gingival and middle thirds of the tooth. This produces
a
more esthetic result and may decrease the torqueing forces
transmitted to the abutment.
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Retentive Arm
Reciprocal Arm
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Interferences:• Certain structures within the oral cavity may
interfere with the
insertion of a removable partial denture. These structures
may
include teeth, bony prominences, soft tissue undercuts, and
exostoses.
• In some instances, difficulties may be avoided by changing
the
tilt of the cast on the surveying table. In other instances,
surgical intervention may be necessary to correct
undesirable
contours.
• Interferences in the maxillary arch.
o Palatal Torus: Changing the tilt of the cast on the
surveying table will not solve the problem. The design of
the major connector may be altered to accommodate the
torus. If this is not possible, surgical removal of the
torus
should be accomplished.
o Exostoses and undercuts are common on the buccal
surfaces of the maxillary arch Buccal exostoses and
undercuts prevent intimate contact between the removable
partial denture and the patient’s soft tissues. Surgical
correction is simple and should be accomplished to
provide an improved restorative prognosis.
o Facial tipping of posterior teeth may cause significant
difficulties. As a maxillary posterior tooth tips facially, the
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height of contour moves toward the occlusal surface. This
makes positioning the buccal clasp arm more difficult for
esthetic and mechanical reasons.
o Undercut in the edentulous maxillary anterior ridge
• Interferences in the mandibular arch.
o Mandibular Tori: Such tori are difficult to avoid because
of the anatomy of the mandibular arch. If the delicate
tissues overlying mandibular tori must be crossed, space
must be created between these tissues and the inner
surfaces of the major connector. Surgery is a common
consideration in this case.
o Lingual tipping of mandibular posterior teeth.
o Bony prominences are often encountered at the facial
surfaces of mandibular canines and premolars.
o Soft tissue undercuts.
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Esthetics:
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To obtain optimum esthetics in removable partial denture
therapy:
(1) Metal components must be concealed as possible: By
choosing the appropriate tilt, they can be disguised while
maintaining the health of the associated soft tissues.
(2) Prosthetic teeth must be selected, contoured, and
properly
positioned: Due to tooth migration, prosthetic teeth will
have
to display smaller mesiodistal dimensions to fit into the
reduced amount of space. This may result in:
a) Esthetic compromise, particularly in anterior regions.
b) Undesirable undercuts will form.
Management could be by:
o Recontouring the proximal surfaces of teeth.
o If recontouring is not possible, then crowns or other
suitable restorations should be planned.
The surveyor is a necessity here in:
✓Determining the amount of recontouring needed to reduce
undesirable undercuts.
✓Determining the final tilt of the cast should consider this
problem.
Guiding Planes:
Are parallel surfaces of abutment teeth that direct the
insertion
and removal of a partial denture.
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Guiding planes are formed from the proximal tooth surfaces
of
the teeth and are contacted by the minor connectors or other
rigid components of the partial denture.
The guiding planes are in intimate contact with the minor
connectors, help to stabilize against the lateral forces. They
also
help protect weakened teeth from potentially destructive
lateral
forces.
Path of Insertion
❖The tilt of a cast determines the direction that the partial
denture will take during placement and removal. The resultant
pathway is termed the path of insertion.
❖ For practical purposes, the path of insertion and removal will
always be parallel to the vertical arm of the surveyor.
❖Most removable partial dentures have two or more paths of
insertion.
❖Tooth bounded edentulous spaces determines whether a prosthesis
will have one or more paths of insertion.
❖ In unmodified Kennedy Class I & II arches, a prosthesis
may enter or exit its intended position at a variety of angles.
❖ In Kennedy Class II arch with a tooth-bounded modification
space on the opposite side of the arch, the modification space
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will determine the path of insertion. If guiding planes have
been prepared on the proximal surfaces of abutments on the
tooth-bounded side, the prosthesis will display a single path
of
insertion.
❖ In Kennedy Class III & IV arches, the existing edentulous
spaces are entirely tooth bounded. So, the associated
prosthesis
will usually exhibit a single path of insertion.
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Placing Survey Lines▪ Proper placement of survey lines is
essential to the design
process and must be accomplished with great care.
▪ To place survey lines, a carbon marker is positioned in
the
surveyor’s mandrel, and the mandrel is tightened. The
vertical
arm of the surveyor is unlocked to ensure free movement.
▪ Survey lines are transferred to the teeth by maintaining
light
contact between the carbon marker and the cast. Survey lines
are transferred to soft tissue areas in a similar manner.
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▪ This process is continued until the required survey lines
have
been clearly marked on facial and lingual surfaces of the
cast.
Locating and Marking Measured Undercuts
▪ Mechanical undercuts must be accurately located and
appropriately marked to permit correct placement of
retentive
clasps.
▪ The depth and position of the desired undercut will vary
with
the material and clasping system to be used. This will allow
the
practitioner to choose the appropriate undercut gauge and
identify the position of the required undercut.
▪ Upon selection of the appropriate undercut gauge, the gauge
is
inserted into the mandrel and locked into place. The
surveying
table is then positioned so that the selected abutment tooth
contacts the shank of the undercut gauge.
▪ The vertical arm of the surveyor is raised until the head of
the
undercut gauge lightly contacts the infrabulge area of the
tooth.
▪ The point of contact should appear as a very light “scrape”
on
the surface of the cast. The apical border of this contact
should
be clearly marked using a red pencil and should appear as a
thin, horizontal line approximately 2 mm in length.
TRIPODING:
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✓Once tilt has been selected for given RPD design, this tilt
should be preserved, so that it can be re-established accurately to
the
surveying table.
✓This procedure is termed as “TRIPODING". This helps in
returning the cast to the surveyor for future reference.
METHODS FOR TRIPODING A CAST
METHOD 1: By placing widely spaced dots on the tissue surface
of
the cast using the tip of the carbon marker, with the vertical
arm of
the surveyor in a locked position.
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METHOD 2:
Scour 2 sides and the dorsal aspect of the base of the cast with
a
sharp instrument/ marking pencil held against the surveyor
blade.
Marks don’t interfere with the design
Easy duplication PG. ! 11
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May get smudged upon handling.
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METHOD 3
A hole about 10 mm in diameter and 10 mm deep is prepared in
the
lingual land area of the mandibular cast with a large acrylic
finishing
bur.
The pin is locked in the vertical spindle and lowered to the
bottom
of the hole.
The vertical spindle with the pin is then locked in this
position and
the hole is filled with dental plaster.
Once the plaster is set, vertical spindle is released from
cemented
pin.
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Step by Step Procedures in Surveying a Diagnostic Cast:
Orientation of cast.
Cast tilting.
Visual analysis using analyzing rod.
Marking of survey lines /soft tissue undercuts using carbon
markers.
Undercut gauges used to measure amount of available
retention.
Interferences.
Wax Trimmers.
Tripoding of casts.
For further references:
Stewart's Clinical Removable Prosthodontics, Chapter 7
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